(a) Technical Field
The present invention provides an apparatus and a method for producing lactic acid. In one aspect, it relates to an apparatus and a method for economically producing D-type lactic acid that can be used as raw material for making D-type poly-lactic acid, which can be used as a starting material for producing a stereo-complex poly-lactic blend, a highly potential plant-based material useful as a decoration material for interior/exterior of a vehicle.
(b) Background of the Invention
Among biomass polymers, poly-lactic acid (PLA) is a linear aliphatic polyester and a thermoplastic polymer material, which can be synthesized using monomers obtained from 100% reproducible resources, such as, potato starch and corn starch.
Lactic acid has two stereoisomers, L-type and D-type, with different optical activities. D-type lactic acid can be used for manufacturing D-type poly-lactic acid, which can be used for producing the stereo-complex poly-lactic acid blend, a plant-based material useful to decorate the interior/exterior of a vehicle.
Korean Patent Application Publication No. 2010-0110345 discloses a method for producing lactic acid at a low cost through a continuous fermentation. The lactic acid as produced has a long-term storage stability.
The above mentioned reference discloses, as demonstrated in FIG. 1, a method for producing lactic acid including the steps of: producing a fermentation liquor by adding a culture medium and a neutralizing agent into a fermenter for fermentation; removing microorganisms from the fermentation liquor using a porous membrane filter with an average pore-diameter ranging from 0.01 μm to 1 μm; and extracting lactate from the filtered liquid (i.e., the fermentation liquor) where the microorganisms are removed, and recycling non-filtered liquid by adding into the fermenter for fermentation. In this process, a yeast is used as a microorganism for fermentation, and a culture medium equivalent in volume to that of the extracted fermentation liquor is added into the ferementer.
However, the use of a yeast for the lactic acid fermentation requires a neutralization step because the yeast is vulnerable to acidic conditions that would be caused by produced lactic-acid. Moreover, the synthesis of poly-lactic acid requires an additional process, which involves replacing lactic acid with neutralized lactate, thereby increasing the manufacturing cost. Further, as protein and sugar sources will remain in the filtered liquid in the fermenter, the excess sources also attribute an increased cost for raw materials.
The above information disclosed in this Background section is intended only for a better understanding of the present invention. At no time, it may be construed as the Applicants' admission of the prior art that is apprised by a person of ordinary skill in the art.